1. Field
The present disclosure generally relates to techniques and equipment for fabricating airfoils such as wings and stabilizers, and deals more particularly with a method and apparatus for fabricating large scale integrated airfoils formed from composites.
2. Background
Large scale composite airfoil structures, such as wing boxes may be built up using fasteners to mechanically assemble multiple composite components. The use of fasteners has a number of disadvantages, including but not limited to increased part count, higher labor costs for fastener drilling and assembly, added weight to the structure and the susceptibility of fasteners to lighting strikes.
Some of the disadvantages of mechanical assembly using fasteners may be overcome by integrating composite components to reduce part count, however large scale integration of composite structures may present several challenges. For example, although large scale integration may reduce the number of parts, some parts may require special storage, handling and tracking prior to a final bonding operation. These requirements can in turn increase work in process (WIP), tool turns and freezer storage space. Also, the tooling required for large scale integration may be relatively complicated, heavy and costly. For example, it may be difficult to achieve the desired dimensional control of large scale integrated structures without the use of complicated and expensive matched die tooling. Additionally, final bond tooling may require additional heavy and expensive reinforcement structures in order to withstand the forces imposed by autoclave processing.
Large scale integrated structures may require a correspondingly large area of vacuum bagging, which may be labor intensive to install and may present the opportunity for bag leaks that may be difficult to detect and repair prior to curing. Still another challenge presented by large scale integration involves the fact that certain NDI (non-destructive inspection) operations may be carried out only after final cure. NDI performed after the final cure step may not allow early detection of parts requiring rework, and may result in expensive repairs or scrapping of a relatively large part or assembly due to a nonconformity in a relatively small portion.
Accordingly, there is a need for a method and apparatus for fabricating large scale integrated composite structures such as airfoils that reduce the need for large, expensive and/or complicated tooling to maintain dimensional control over assembled parts, while reducing the amount of vacuum bagging that is required during final cure operations. There is also a need for a method and apparatus as mentioned above which may allow early detection of parts requiring rework before they are integrated into a final structure and which may avoid the need to subject large assembled parts to autoclave pressures.